#include<bits/stdc++.h>
#define int long long
using namespace std;

const int B=11451419191,mo=1145141919810114557;
int n;
string s[2];
int qh[2][1000001],bh[2][1000001],po[1000001];

inline int HASH_A(int x,int l,int r){
return ((qh[x][r]-(__int128)qh[x][l-1]*po[r-l+1])%mo+mo)%mo;
}

inline int HASH_B(int x,int l,int r){
return ((bh[x][l]-(__int128)bh[x][r+1]*po[r-l+1])%mo+mo)%mo;
}

signed main(){
std::ios::sync_with_stdio(false),cin.tie(0);

cin>>n;
cin>>s[0]>>s[1];
s[0]=" "+s[0]+" ";
s[1]=" "+s[1]+" ";
po[0]=1; for (int i=1;i<=n;++i) po[i]=(__int128)po[i-1]*B%mo;

for (int i=0;i<2;++i){
for (int j=1;j<=n;++j) qh[i][j]=((__int128)qh[i][j-1]*B+s[i][j])%mo;
for (int j=n;j;--j) bh[i][j]=((__int128)bh[i][j+1]*B+s[i][j])%mo;
}

int ans=0;

for (int i=1;i<=n;++i) for (int j=i;j<=n && j<=i+1;++j){
int lt=0,rt=min(n-j,i-1),d=0;
while (lt<=rt){
int md=(lt+rt)>>1;
if (HASH_A(0,i-md,i)==HASH_B(0,j,j+md)) d=md,lt=md+1;
else rt=md-1;
}
lt=1,rt=min(n-j+1,i-1)-d; int aa=0;
while (lt<=rt){
int md=(lt+rt)>>1;
if (HASH_A(0,i-d-md,i-d-1)==HASH_B(1,j+d,j+d+md-1)) aa=md,lt=md+1;
else rt=md-1;
}
if (s[0][i]==s[0][j]) ans=max(ans,2*(d+aa)+(i==j?1:2));

lt=0,rt=min(n-j,i-1),d=0;
while (lt<=rt){
int md=(lt+rt)>>1;
if (HASH_A(1,i-md,i)==HASH_B(1,j,j+md)) d=md,lt=md+1;
else rt=md-1;
}
lt=1,rt=min(n-j,i)-d; aa=0;
while (lt<=rt){
int md=(lt+rt)>>1;
if (HASH_A(0,i-d-md+1,i-d)==HASH_B(1,j+d+1,j+d+md)) aa=md,lt=md+1;
else rt=md-1;
}
if (s[1][i]==s[1][j]) ans=max(ans,2*(d+aa)+(i==j?1:2));
}

for (int i=1;i<=n;++i){
int lt=0,rt=min(i-1,n-i),aa=-1;
while (lt<=rt){
int md=(lt+rt)>>1;
if (HASH_A(0,i-md,i)==HASH_B(1,i,i+md)) aa=md,lt=md+1;
else rt=md-1;
}
ans=max(ans,2*aa+2);
}

cout<<ans<<'\n';

return 0;
}